A semiconductor LED is known as a next generation light source having the advantages of a long life span, low power consumption, fast response time, high power output, and the like in comparison to a conventional light source, and is currently has prominence as a light source useful for various products.
In an LED-using light emitting device, a technique using phosphors is widely employed in order to convert light emitted from an LED chip into light of a different wavelength. More particularly, such a wavelength conversion technique is required in order to generate white light used for various types of lighting apparatuses and the backlight units of display devices.
In a wavelength-converted light emitting device for the production of white light, phosphors are contained in a transparent resin encasing an LED chip to convert a portion of the original light emitted from the LED chip into secondary light of a different wavelength. The wavelength-converted light emitting device can produce white light by mixing an unconverted portion of the original light with the secondary light.
The transparent resin mixed with the phosphors is provided to surround the LED chip. In this case, the distribution of the phosphors provided to convert a light wavelength can have an influence on the brightness of emitted white light and the light spectrum. That is, when the phosphors are not uniformly distributed inside a resin encasing portion, light emitting efficiency deterioration and hue deviation by far field beam distribution may occur. In addition, when two or more kinds of phosphors (for example, a combination selected from yellow, green, an red phosphors) are used to improve a color rendering index (CRI), a problem due to the non-uniform distribution of phosphors may become more serious.
More particularly, in a light emitting device having a high flux LED driven by a high current, the distribution of irregular phosphors having a low reproduction rate has the disadvantage of accelerating the color conversion efficiency reduction rate and the reliability reduction rate to an even greater degree.